It is a common practice to incorporate a cationic high-molecular electrolyte in a hair cleansing composition such as a shampoo so that physical properties of its foam are modified to improve touch in use during washing and to improve finger combing upon rinsing. For example, there have been proposed hair cleansing compositions containing anionic surfactants, amphoteric surfactants, cationic guar gum or nonvolatile silicones (WO 97/41827) and hair cleansing compositions containing ethoxylated organic carboxylic acid anionic surfactants, cationic derivatives of polygalactomannan gum, polysiloxane droplets, or organic carboxylic acids or salts thereof (JP-A-2001-10934). With these techniques, however, fully satisfactory performance has not been obtained yet with respect to foamability and foam lubricity upon washing and smoothness upon rinsing.
In hair treatments such as hair rinses and hair conditioners, it is also practiced to lower the pHs of their systems to impart luster and softness to hair. No attempt has, however, been made to lower the pHs of hair cleansing compositions, because the hair cleansing compositions are intended to impart neither luster nor softness in general.
With a view to providing hair cleansing compositions with such a luster and softness-imparting function as described above, the present inventors conducted research on low-pH hair cleansing compositions which made use of organic acids. A problem, however, arose in that in a low pH range, anionic surfactants as cleansing ingredients underwent decomposition, resulting in stability deteriorations such as gelling of systems and reductions in foamability.